Broad energy-range ribbon ion beam collimation using a variable-gradient dipole

ABSTRACT

A method and apparatus satisfying growing demands for improving the intensity of implanting ions that impact a semiconductor wafer as it passes under an ion beam. The method and apparatus are directed to the design and combination together of novel magnetic ion-optical transport elements for implantation purposes for combating the disruptive effects of ion-beam induced space-charge forces. The design of the novel optical elements makes possible: (1) Focusing of a ribbon ion beam as the beam passes through uniform or non-uniform magnetic fields; (2) Reduction of the losses of ions comprising a d.c. ribbon beam to the magnetic poles when a ribbon beam is deflected by a magnetic field.

This Application is a continuation of U.S. patent application Ser. No.11/289,863 filed Nov. 30, 2005 now U.S. Pat. No. 7,414,249, which claimspriority to U.S. provisional patent application Ser. No. 60/631,655filed Nov. 30, 2004 entitled “Broad Energy-Range Ribbon Ion BeamCollimation Using a Variable-Gradient Dipole” the disclosures of whichare incorporated herein by reference in its entirety.

FIELD OF INVENTION

The disclosed methods and apparatus relate generally to the constructionand use of magnetic focusing and correction elements for modifying theintensity distribution of ions within ribbon beams and more particularlyto the introduction of magnetic-field modification coils that can beadded to uniform and non-uniform field magnetic dipole deflectors forproviding auxiliary variable magnetic field focusing and the reductionof the effects of space-charge forces.

BACKGROUND OF THE INVENTION

The process of ion implantation is a critical manufacturing element usedby the semiconductor industry. Implantation makes possible precisemodification of the electrical properties of well-defined regions of asemiconducting work-piece by introducing selected impurity atoms, one byone, with a velocity such that they penetrate the surface layers andcome to rest at a specified depth below the surface. The characteristicsthat make implantation such a useful processing procedure are threefold:First, the concentration of the introduced charged dopant atoms can beaccurately measured by straight-forward integration of the incomingelectrical charge delivered to the work-piece; secondly, the patterningof dopant atoms can be precisely defined using photo-resist masks;finally, the fabrication of layered structures becomes possible byvarying the ion energy.

The ion species used for silicon implantation include arsenic,phosphorus, germanium, boron and hydrogen. The required implant energiesrange from below 1 keV (kilo-electron volts) to several hundred keV. Ioncurrents used range from microamperes to multi-milliamperes. Projectingto the future, demands are for greater productivity (elevated ionintensities); implantation at energies well below 1 keV; improvedprecision of uniformity and ion-incidence angle-control at the wafer.

During the last decade there has been an industry shift towards the useof D.C. ribbon-beams. This technology arranges that dopant ions arriveat a semiconducting wafer as part of a uniform-intensity beam that isorganized into a long, small-height stripe that simultaneously implantsuniformly the whole width of a semiconductor wafer. This geometry makespossible uniform implantation of a wafer during a single pass under theribbon beam. The advantages of ribbon beam technology are substantial:(1) Batch implantation of multiple wafers and the use of large spinningdiscs is no longer necessary as the energy density at the wafer is low.(2) Wafers move slowly along a single linear path, avoiding issues ofdamage to delicate circuit components related to collision of heavyparticles that arrive at the wafer surface.

U.S. Pat. No. 5,350,926 entitled “High current ribbon beam ionimplanter” and U.S. Pat. No. 5,834,786, entitled “Compact high currentbroad beam ion implanter”, both issued to N. White et al., presentaspects of ribbon beam technology. Implanters, generally designedaccording to these principles, are manufactured by Varian SemiconductorEquipment Associates of Gloucester, Mass.

Referring to FIG. 2 it can be seen that in a typical ribbon beam tool afirst magnetic deflector directs wanted-mass ions through amass-resolving aperture where unwanted species from the ion source arerejected. Downstream of this aperture the emitted fan-shaped beam, nowcomprising only wanted ions, is parallelized by a second magnet andtransformed to the ribbon length needed for implanting a specific waferdiameter. A deceleration system beyond the mass rejection aperture isincluded to reduce the energy of ions arriving at the wafer; the purposebeing to allow the use of ion source extraction energies that are bestsuited for efficient source extraction and high transmission efficiencythrough the mass-resolving aperture.

In a ribbon beam implanter the control of space charge is a centralissue. These effects are manifest mainly downstream of the decelerationregion and are particularly troubling in the region of the secondmagnetic deflector where the presence of a magnetic field makes itdifficult for the beam potential to trap the necessary neutralizingelectrons: Captured electrons have difficulty moving across the magneticfield lines but can easily escape to the poles unless some form ofelectron trapping is present. Also, there is evidence that electrontemperatures grow within magnetic fields further increasing electronlosses. Thus, as a consequence of inadequate neutralization, theboundaries of the beam tend to expand allowing ions to be intercepted atthe magnet poles or at the walls of the vacuum chamber.

Space charge problems have been recognized since the days of theManhatten Project's development of the Uranium Bomb. An historicalreview, including the impact of space charge on that project, has beenwritten by William E. Parkins and published on page 45 of the March 2005edition of the magazine Physics Today. Further background for theseprocesses can be found in a book entitled ‘Large Ion Beams’ written byA. T. Forrester and published by John Wiley and Sons in 1988. The abovereferenced book presents data and calculations on pages 139 to 153concerning the manner in which ions ‘peel away’ from the outside of adrifting low-energy ion beam. In addition, data is included concerningthe difficulties of achieving space charge neutralization withinmagnetic fields and the manner in which the ion-beam potential is raisedas it passes through a magnetic field. Other authors who discuss spacecharge effects include V. Dudnikov in U.S. Pat. No. 6,329,650 and F.Sinclair, et al. in U.S. Pat. No. 5,814,819.

The solution which provides at least partial neutralization of theeffects of space-charge expansion depends upon the fact that the sameelectric field distribution that causes the boundaries of a positive ionbeam to expand because of space-charge effects is also an electric fielddistribution that attracts negative ions or electrons towards the centerof an ion beam. However, even when created within the beam potentialitself, these electrons tend to concentrate near the center of thepositive ion beam leaving peripheral regions somewhat short ofelectrons, causing a tendency for ions to ‘peel-away’ from the outeredges of a ribbon beam. This peeling effect will be accentuated by thefields generated between image charges at the surface of a narrow vacuumenvelope and non-neutralized positive ions within the beam itself.

In the energy range above ˜15 keV interactions between fast beam ionsand residual gas molecules usually provides sufficient secondaryelectrons that the space-charge density of the ion beam is largelyneutralized. However, magnets whose focusing properties are satisfactoryfor deflecting ion beams having energy above ˜15 keV may not provideacceptable transmission in the energy region below 5 keV, due to theabove space charge effects. Additional magnetic field components may beneeded for compensating residual space charge effects and for improvingbeam transmission through magnetic fields, the central theme of thepresent patent disclosure.

SUMMARY

Historically, the design of most existing commercial implanters includesmagnetic deflectors that have predetermined ion focusing properties.These properties are established by the shapes of the coils and themagnet poles and generally can only be adjusted in a minor way, if atall, during implanter operation. Thus, when space-charge forces cause anexpansion of the outer beam boundaries and consequent ion interceptionat the vacuum chamber or magnetic poles there is no procedure forintroducing compensating compression forces.

The present patent disclosure describes a method and apparatus forsuperimposing variable magnetic focusing fields onto a uniform orindexed dipole deflecting field. These additions, thought of asperturbations to the main dipole field, are designed to introducecompression effects that provide approximate compensation forout-of-the-median-plane space charge expansion forces present inlarge-width ribbon beams. (Increases in ribbon length can be adjustedusing other procedures). It will be recognized by those familiar withthe art that, provided saturation does not occur, the magnetic fieldsnecessary to produce supplemental focusing can be adjusted with littleeffect on the underlying dipole contribution allowing such perturbingfields to be increased or decreased at will and be turned on only whenrequired for low-energy operation.

It has previously been confirmed that such active focusing elements canbe useful during magnetic mass analysis when compensation is needed forcombating the disruptive effects of space charge. In a patent disclosureby V. M. Benveniste in U.S. Pat. No. 5,554,827 entitled “Method andApparatus for Ion Beam Formation in an Ion Implanter” an apparatus forfiltering unwanted particles from a narrow ion beam compensatesspace-charge effects by adding adjustable quadrupole fields to a basicdipole field. Space charge expansion is compensated for circularcross-section ion beams by superimposing blocks of independentlyadjustable magnetic quadrupole fields along the centerline of thedeflected ion beam locus, defined by the dipole field needed forconventional mass separation. However, when the transverse dimensions ofthe ion beam become comparable to the radius of curvature in the dipolefield, as is the case for a broad ribbon beam, the above quadrupolefield method does not have desirable linear optical transportproperties.

Both positive and negative quadrupole and sextupole focusing fields havebeen widely used as beam transport elements. Techniques for introducingselected multipole field components into a single beam transportcomponent has been described in an article entitled “The design ofmagnets with non-dipole field components”, authored by N. White et al.and published in the journal Nuclear Instruments and Methods, volumeA258, (1987), pages 437-442. A supplementary publication authored byHarald A. Enge entitled ‘Deflecting Magnets’, found on pages 203-264 ofVolume II of the book entitled ‘Focusing of Charged Particles’, editedby A. Septier, and published by Academic Press (1967), describes theoptical properties of indexed magnets.

The introduction of variable positive focusing in the y-direction of anindexed collimating magnet is the objective of the present invention. Asbackground the above referenced article by Enge points out that if thedeflecting magnetic field at the median plane, B(r), has the formB(r)=B ₀(r/R ₀)^(−n)the optical transfer characteristics are identical to those of linearoptical lenses. [Here, B₀ is the field at the central trajectory (atradius R₀), r is the radius where the field is measured and n is theindex of the field-gradient]. When n=0 the deflecting magnetic field isuniform; when n is made negative, defocusing is introduced totrajectories traveling in the median plane and positive focusing isintroduced to trajectories traveling in planes at right angles to themedian plane (the y-direction); when n is positive focusing is reversed.

In the present invention, which is primarily related to efficientcollimation of large width ribbon beams, pole-face windings have beenintroduced to modify the basic dipole field index and add additionalvariable positive focusing in the y-direction. The pole-face windingsconsist of a multiplicity of different area coils, (ampere-turngenerators), that are mounted on or recessed into the pole surfaces. Inthe preferred embodiment the shape of an individual coil is defined by asingle conductor oriented approximately along the ion-beam path with itsends being coupled to radial conductors that extend beyond the insidecurved boundaries of the magnetic pole. Here, the radial conductors areconnected to a suitable power source or connected in series or parallelwith other coils. If necessary, individual coils may consist of severalturns connected in series or parallel to increase ampere turns and thusthe magnetic field gradient developed across the pole.

The key to introducing a supplementary field gradient is that theensemble of subsidiary windings do not completely overlap each other butrather are wound as a stepped structure across the whole width of themagnet pole with the maximum coil overlap and thus the additionalfocusing magnetic field being a maximum on the inside of the curve and aminimum at the outside. The spacing between windings establishes thelocal shape of the n-value gradient which those skilled in the art willrecognize does not have to be identical to that of the underlying dipoleindex. In this manner, the uniform magnetostatic potential differencebetween the poles of the underlying dipole field is modified to become adistribution that varies as a function of the radius, producing avariable field distribution that enhances or subtracts from the in-builtfocusing of the underlying indexed-dipole collimation magnet.

While an aberration-corrected single-index magnet is most appropriatedesign for the collimator magnet shown in FIG. 2 it will be recognizedby those skilled in the art that by arranging multiple regions along theion path where the n value of a deflection magnet changes at least oncefrom positive to negative, or vice versa, overall positive focusing canbe introduced that will simultaneously provide positive focusing in boththe median plane and the direction at right angles.

BRIEF DESCRIPTION OF THE DRAWINGS

For better understanding of the present invention, reference is made tothe accompanying drawings which are incorporated herein by reference:

FIG. 1 A Beam Coordinate System

FIG. 2 Optical Schematic for a Simplified Ribbon Beam Implanter.

FIG. 3 Tapered Gap Focusing

FIG. 4: Supplemental Field Generation

FIG. 5: Single Supplemental Field Distribution

FIG. 6: Dual Supplemental Magnetic Field Generation

FIG. 7 Pole-Face Windings

DETAILED DESCRIPTION

FIG. 1 illustrates the beam coordinate system used in the followingdiscussions. The X-axis is always aligned with the front surface of theribbon-beam, 120, and along the beam's long axis. The Z-axis istangential to the central trajectory of the ribbon beam, 110, and isalways coincident with the central trajectory. At each point along thebeam path the orthogonal Cartesian Y-axis also lies in the surface, 120,and along the ribbon beam's narrow dimension.

FIG. 2 presents a schematic of the preferred embodiment of a D.C.ribbon-beam implanter. It can be seen that there are two magneticdeflections along the beam path, 201 and 202. The first magneticdeflection, 201, directs wanted-mass ions leaving the ion source, 220,through a mass-resolving aperture, 203. Unwanted species, 210, arerejected at the walls of the vacuum chamber or at the mass-resolvingaperture, 203. The selected ions, 204, are directed into the succeedingoptical elements, 211 and 202, comprising a deceleration stage, 211, anda collimating magnet, 202. The collimating magnet, 202, rejectshigh-energy neutral particles generated in the deceleration gap. It alsoprovides the positive focusing needed for transforming the diverging ionbeam passing through the mass selection slit, 203, to substantiallyparallel trajectories at the wafer implantation location, 206.

Referring again to FIG. 2 it can be seen that the wanted ions leavingthe source pass through the opening between the jaws of the massrejection slits, 203, to form a well-defined source of wanted ions fromwhich almost all of the background particles, 210, have been removed.The opening between the mass rejection slits, 203, is shaped to matchthe emittance of the ion beam; namely, a narrow cross section of thebeam in the horizontal dispersive plane and a tall aperture at rightangles in the non-dispersive direction. The transmitted beam throughthis slit has the form of a uniform fan when viewed from above the x-zplane. The fan of ions, 204, subtends an angle at the mass slitnecessary to form the desired ribbon-beam length at the wafer plane,206. In the out-of-plane direction the trajectories of ions transmittedthrough the aperture 203, are substantially parallel to the x-z plane.On leaving the mass resolving slit, 203, the ions drift for a shortdistance and then enter the deceleration region, 211. Here, ions areretarded to the energy required for implantation at the wafer, 206. Animportant function of this deceleration stage, 211, is to allowextraction of ions from the ion source at energies that are best suitedfor efficient ion-source extraction and high transmission efficiencythrough the mass resolving slit.

Referring again to FIG. 2 it can be seen that the ions leaving thedeceleration region, 211, are directed into the collimator magnet, 202.Here, the positive optical strength of this magnetic deflector, 202,transforms the fan-shaped beam to a group of parallel trajectoriesrequired for implantation at the wafer, 206.

FIG. 3 shows how focusing that can be introduced in a deflection magnetif the radial gap between the poles, 301, 302, is tapered radially. Itcan be seen that, because the pole surface represents an equipotential,in the z-direction (out of the page) the field acting on the trajectory310, is less than that acting on the trajectory 311, causing thedeflection radius of curvature to be greater for trajectory 310 than for311. Thus, focusing in the x-direction is weakened, compared to thatobserved in a uniform field magnet; negative focusing has beenintroduced to the median plane trajectories. In the vertical directionit can be seen that, because of symmetry, the magnetic field lines, B,must cross the median plane, 304, normally. Away from this plane, in they-direction, an x-component of the deflecting field develops with thisx-component increasing linearly with the y-distance away from the medianplane, 304, changing sign at the median plane. The effect is theproduction of a focusing field component in the direction along thedipole field lines that increases linearly with distance from the medianplane. It can be seen that as positive focusing in the x-z plane isreduced, positive focusing in the y,z plane increases correspondingly.

Referring again to FIG. 3, it should be emphasized that ability toactively vary the index of the magnetic deflection field—the shape ofthe tapered opening between the poles—can be used to provide acompensating compressive effect upon ion beams that are expandingtowards the poles and losing ions there because of the effects ofspace-charge forces.

It will be recognized by those skilled in the art that by arrangingthat, along the ion path of a deflection magnet, the field index of thetapered pole gap changes at least once from positive to negative ornegative to positive, positive focusing can be introduced in both themedian plane and the direction at right angles.

FIG. 4 shows an embodiment of the principles used to produce the fielddistribution needed for introducing variable focusing of a ribbon beamand the beam compression needed to minimize space-charge effects. It canbe seen that a series of ever decreasing-area coils, 401, 402, 403, 404,etc, each enclosed by a conductor, or a plurality of conductors havingthe same shape, are superimposed layer by layer, so that the ampereturns generated by each layer add together in those regions where layersoverlap to produce a perturbing field. Arrangements of such overlappingcoils can be used to modify the base dipole-field index and add variablepositive focusing in the y-direction.

The key to introducing such supplementary field gradients is that theensemble of subsidiary windings do not completely overlap each other butrather are wound as a stepped structure across the whole width of themagnet pole. In one embodiment the overlapping coils will have a maximumnumber sections overlapping on the inside of the ion beam deflectioncurve and a minimum number of sections along the outside of the curve.

The preferred embodiment involves the use of the above field generatingtechnology but extends the concept in-as-much as the zero perturbingfield regions are present along the ribbon-beam center-line, instead ofat one edge of the ribbon beam as described above. Using this geometry,two supplementary field maxima are generated: One is on the inside andthe other on the outside of the ribbon beam. It should be emphasizedthat the current direction through coils on the two sides are such thatthe sign of the supplementary magnetic field perturbations are positiveon one side of the central trajectory and negative on the other. Thesetwo maxima can be controlled independently to introduce higher orderdeflections. Those skilled in the art will recognize that even higherorder contributions can be introduced by individually varying thecurrent passing through individual loops.

Referring again to FIG. 4 it can be seen that an increasing fieldperturbation is typically defined by a group of single conductors, 410,411, 412, 413 etc. that are approximately oriented along the directionof the ion-beam. The ends of each of these conductors are coupled toradial wires, 420, that extend across the width of the underlyingmagnetic pole to regions outside the curved boundaries of the magneticpole. Here, the radial conductors are connected to a suitable powersource or connected in series or parallel with other coils. In thepreferred embodiment the conductor 410 would be close to the centraltrajectory. Referring again to FIG. 4 it can be seen that a growingmagnetic B-field pattern is created for equal loop currents when thespacing of the conductors 410, 411, 412 and 413 etc. increases linearlyas a function of radial location. However, it should be noted thatnon-uniform spacing can lead to the introduction of sextupole andoctopole contributions. It should also be noted that it is possible topower the above element individually or in groups making possible activeintroduction of higher order corrections. It can be seen that theuniform magnetostatic potential difference between the poles of theunderlying dipole field is thus modified by the supplementary coilswhich produce a distribution that can be varied as a function of theradius. Such changes enhance or subtract from the in-built focusingindex of the underlying dipole magnet.

FIG. 5 shows schematically the method for generating supplementalmagnetic fields that complements an underlying uniform dipole field. Asan example, the underlying field for a uniform magnetic field would havethe value shown by the dotted line, 503, across the width of the pole.The stacking of the coils is illustrated schematically as the layeredpattern, 501, to produce the total field vectors across the pole, 511.It can also be seen that in its simplest embodiment the auxiliary fieldsintroduce an additional component to the dipole field at the center ofthe pole, 506, having the differential increase, 510.

FIG. 6 shows a second embodiment. It will be seen that the stacked fieldgenerators, described previously in FIG. 4, are divided into two sectionwhich are placed end-to-end with zero height close to the centraltrajectory. The stacked generators, 601, have currents circulating in adirection that enhances the field, 603, developed by an underlyinguniform-field dipole magnet. The second set, 602, are shownschematically below the magnetic-field zero line to indicate that thecurrents through these coils circulate in the opposite direction to thatof the coils, 601, producing a further supplementary field pattern thatreduces the underlying dipole field.

FIG. 7 shows the preferred embodiment as applied to wafer implantation,703, 206. Variable supplementary focusing fields are added to the fieldsgenerated by an underlying indexed or uniform dipole magnet, 202, 705.It can be seen that the auxiliary magnetic-field generating coils aresymmetrically disposed about the central beam trajectory, 702, andconsist of a number of circumferential conductors mounted directly onthe magnetic poles, 705, or recessed into shallow slots machined intothese poles. The conductors located in trenches, 710, are connected tothe power sources, 701, 704 by suitable radial current feeds locatedalong the sides of the magnet pole, as shown. Those skilled in the artwill recognize that it may be necessary to hide these conductors in amanner that arranges that residual fields be shielded from the beam.Through each of these coils, which may consist of several turns,currents circulate in the directions shown by the arrows, 711.

1. A method of modifying trajectory angles in the x-z and y-z planes ofa scanned beam or a ribbon beam at locations across its width, said beamhaving a central beam trajectory, comprising: providing a plurality ofregions within a D.C. dipole magnetic field, each of said regionscomprising a plurality of conductive coils whereby each conductive coilis adapted to carry current through two feed conductors and acircumferential conducting section; wherein said feed conductors of saidplurality of conductive coils are all overlapping and eachcircumferential conducting section is substantially concentric about asingle point, where at least one of said circumferential conductingsections is substantially aligned to the path of said central beamtrajectory.
 2. The method of claim 1, wherein each of said feedconductors is substantially aligned at right angles to the central beamtrajectory of said beam.
 3. The method of claim 1, wherein said D.C.dipole magnetic field is produced using a north magnetic pole and asouth magnetic pole and said plurality of coils is positioned on thesurface of one of said magnetic poles.
 4. The method of claim 1, whereinsaid D.C. dipole magnetic field is produced using a north magnetic poleand a south magnetic pole and said plurality of coils is positioned onthe surfaces of said north and south magnetic poles.
 5. The method ofclaim 1, wherein said D.C. dipole magnetic field is produced using anorth magnetic pole and a south magnetic pole and said plurality ofcoils is positioned in apertures recessed into the surface of one ofsaid magnetic poles.
 6. The method of claim 1, wherein said D.C. dipolemagnetic field is produced using a north magnetic pole and a southmagnetic pole and said plurality of coils is positioned in aperturesrecessed into the surfaces of said north and south magnetic poles. 7.The method of claim 1, wherein said D.C. dipole magnetic field isnon-uniform.
 8. The method of claim 1, wherein said D.C. dipole magneticfield is uniform.
 9. The method of claim 1, wherein the radius ofcurvature of each of said circumferential conducting sections isadjusted from coil to coil to produce the desired D.C. dipole magneticfield distribution for a constant current distribution within all coils.10. The method of claim 1, wherein the radius of curvature of each ofsaid circumferential conducting sections is adjusted from coil to coilto produce sextupole and other higher order ion beam deflecting fields.11. The method of claim 1 wherein the radius of curvature of each ofsaid circumferential conducting sections is adjusted from coil to coilto produce a D.C. dipole magnetic field distribution indexed to a chosenn-value.
 12. The method of claim 1 wherein the said plurality of coilsis connected electrically in series and is driven by a suitable powercontroller.
 13. The method of claim 1 wherein said plurality of coils isconnected electrically in parallel and is driven by a suitable powercontroller.
 14. The method of claim 1 wherein each of said plurality ofoverlapping coils is driven by an independent power controller.
 15. Themethod of claim 1, wherein said plurality of overlapping coils isconfigured as a plurality of groups, each of said groups being driven byan independent power controller.
 16. An apparatus for modifyingtrajectory angles in the x-z and y-z planes of a scanned beam or aribbon beam at locations across its width, said beam having a centralbeam trajectory, said apparatus comprising a plurality of regions withina D.C. dipole magnetic field, each of said regions comprising aplurality of conductive coils whereby each conductive coil is adapted topass current through two feed conductors and a circumferentialconducting section; wherein said feed conductors of said plurality ofconductive coils are all overlapping and each circumferential conductingsection is substantially concentric about a single point, where at leastone of said circumferential conducting sections is substantially alignedto the path of said central beam trajectory.
 17. The apparatus of claim16, wherein said feed conductors being aligned substantially at rightangles to the central beam trajectory.
 18. The apparatus of claim 16,further comprising a plurality of power controllers, wherein saidplurality of coils is configured as a plurality of groups, each of saidgroups being driven by an independent power controller.
 19. Theapparatus of claim 16, further comprising a plurality of powercontrollers, wherein each of said plurality of coils is driven by anindependent power controller.
 20. The apparatus of claim 16, whereinsaid D.C. dipole magnetic field is produced using a north magnetic poleand a south magnetic pole and said plurality of coils is positioned onthe surface of one of said magnetic poles.
 21. The apparatus of claim16, wherein said D.C. dipole magnetic field is produced using a northmagnetic pole and a south magnetic pole and said plurality of coils ispositioned on the surfaces of said north and south magnetic poles. 22.The apparatus of claim 16, wherein said D.C. dipole magnetic field isproduced using a north magnetic pole and a south magnetic pole and saidplurality of coils is positioned in apertures recessed into the surfaceof one of said magnetic poles.
 23. The apparatus of claim 16, whereinsaid D.C. dipole magnetic field is produced using a north magnetic poleand a south magnetic pole and said plurality of coils is positioned inapertures recessed into the surfaces of said north and south magneticpoles.
 24. The apparatus of claim 16, wherein there are two regionswithin a D.C. dipole magnetic field where the direction of thecirculating currents in individual regions is of opposite hand.
 25. Anapparatus for modifying trajectory angles in the x-z and y-z planes of ascanned beam or a ribbon beam at locations across its width, said beamhaving a central beam trajectory passing through a D.C. dipole magneticfield to form substantially constant angular uniformity across saidwidth of said scanned beam or said ribbon beam, comprising: a northmagnetic pole and a south magnetic pole adapted to produce said D.C.dipole magnetic field; a plurality of regions within said D.C. dipolemagnetic field, each of said regions comprising a plurality ofconductive coils of varying area, each adapted to pass current throughtwo feed conductors and a circumferential conducting section; whereinsaid feed conductors of said plurality of conductive coils are alloverlapping and each circumferential conducting section beingsubstantially concentric about a single point, where at least one ofsaid circumferential conducting sections is substantially aligned to thepath of said central beam trajectory; and a power controller forenergizing at least one of said plurality of coils in at least one ofsaid regions to create an additional magnetic field that can besuperimposed upon said D.C. dipole magnetic field to provide trajectoryangle correction.
 26. The apparatus of claim 25, further comprising aplurality of power controllers, wherein each of said conductive coils isenergized by an independent power controller.
 27. The apparatus of claim25, further comprising a plurality of power controllers, wherein saidplurality of conductive coils is configured as a plurality of groups,each of said group being driven by an independent power controller. 28.An apparatus for modifying trajectory angles in the x-z and y-z planesof a scanned beam or a ribbon beam at locations across its width, saidbeam having a central beam trajectory passing through a D.C. dipolemagnetic fields to form substantially constant uniform trajectoryintensity across said width of said scanned beam or said ribbon beam,comprising: a north magnetic pole and a south magnetic pole adapted toproduce said D.C. dipole magnetic field; a plurality of regions withinsaid D.C. dipole magnetic field, each of said regions comprising aplurality of conductive coils of varying area, each adapted to carrycurrent through two feed conductors and a circumferential conductingsection; wherein said feed conductors of said plurality of conductivecoils are all overlapping and each circumferential conducting sectionbeing substantially concentric about a single point, where at least oneof said circumferential conducting sections is substantially aligned tothe path of said central beam trajectory; and a power controller forenergizing at least one of said plurality of coils in at least one ofsaid regions to create an additional magnetic field that can besuperimposed upon said D.C. dipole magnetic field to provide trajectoryuniformity correction.
 29. The apparatus of claim 28, further comprisinga plurality of power controllers, wherein each of said conductive coilsis energized by an independent power controller.
 30. The apparatus ofclaim 28, further comprising a plurality of power controllers, whereinsaid plurality of conductive coils is configured as a plurality ofgroups, each of said group being driven by an independent powercontroller.
 31. An ion implanter, comprising: a first magnet fordirecting wanted ions through a mass resolving aperture; said apertureconfigured to allow only ions of a desired mass and charge to pass; anda second magnet downstream of said aperture for creating a parallelribbon beam from said ions of a desired mass, comprising a plurality ofconductive coils whereby each conductive coil is adapted to pass currentthrough two feed conductors and a circumferential conducting section;wherein said feed conductors of said plurality of conductive coils areall overlapping and each circumferential conducting section issubstantially concentric about a single point, where at least one ofsaid circumferential conducting sections is substantially aligned to thepath of said central beam trajectory.
 32. The ion implanter of claim 31,wherein said feed conductors being aligned substantially at right anglesto the central beam trajectory.
 33. The ion implanter of claim 31,further comprising a plurality of power controllers, wherein saidplurality of coils is configured as a plurality of groups, each of saidgroups being driven by an independent power controller.
 34. The ionimplanter of claim 31, further comprising a plurality of powercontrollers, wherein each of said plurality of coils is driven by anindependent power controller.
 35. The ion implanter of claim 31, whereinsaid second magnet comprises a north magnetic pole and a south magneticpole and said plurality of coils is positioned on the surface of atleast one of said magnetic poles.
 36. The ion implanter of claim 31,wherein said second magnet comprises a north magnetic pole and a southmagnetic pole and said plurality of coils is positioned in aperturesrecessed into the surface of at least one of said magnetic poles. 37.The ion implanter of claim 31, wherein there are two regions within aD.C. dipole magnetic field where the direction of the circulatingcurrents in individual regions is of opposite hand.